1. Field of the Invention
The present invention relates to a light source device. The present invention also relates to a signal light utilizing a light source device and a light emitting device for a display and others.
The present application is based on the following Japanese Patent Applications, which are incorporated herein by reference: 2000-69800, 2000-93333, 2000-135529, 2000-225572, 2000-294264, 2000-294893, 2000-296052, 2000-296053, and 2000-310634
2. Description of the Related Art
Heretofore, for a light source device used for a signal light, a light source device that has a light bulb as a light source and emits light from a light source via a filter pigmented in each target color such as red and cyan as desired mono chromatic light is generally used. A light source device in which plural lens-type light emitting diodes (LEDs) that emit light of desired color are densely arranged on a board is also known. A light source device having LED as a light source has an advantage that no pseudo-lightening is caused and labor for maintenance can be greatly reduced. In addition, as LED itself emits monochromatic light, external radiation efficiency can be enhanced more than that in a method of using a light bulb that most of emitted light is cut via a filter. Also, in case a filter is used, the color of the filter is displayed by light incident from the outside and may be recognized as if a light source device was turned on, however, in case LED is used for a light source, no filter is required and such pseudo-lightening is not caused. Further, LED is not burn out as a light bulb and has high reliability.
However, as a signal light which has known and has LED as a light source uses lens-type LED as described above, the external radiation efficiency is not enough. The reason is that in lens-type LED, as the directivity is enhanced, loss increases in radiated light and the external radiation efficiency is deteriorated.
Also, to secure sufficient luminous intensity and eliminate the unevenness of emission so that a signal light has satisfactory visibility, LEDs are densely mounted, however, it is troublesome and in addition, as great deal of heat is caused and outgoing radiation is not efficiently performed, LEDs have high temperature. As emission is deteriorated and a life characteristic is deteriorated when LEDs are operated in a state of high temperature, it is not desirable that LEDs are operated in a state of high temperature. Even if the number of LEDs arranged in a fixed area can be reduced by enhancing the output of a light emitting element in future, a problem of the unevenness of emission caused because the mounting number of density of LEDs is reduced, that is, a problem that a signal light does not produce satisfactory visibility is not solved.
Though optics (silver plate on the surface of a lead frame and others) provided to enhance the external radiation efficiency of LED reflects external light and pigmented pseudo-lightening is not caused, it may cause the deterioration of contrast between when LEDs are turned on and when they are turned off.
Reflection-type LED different from lens-type LED is also generally known. As reflection-type LED can utilize light emitted laterally from a light emitting element by reflecting the light on its reflecting surface as external emitted light, it has high external radiation efficiency. As lens-type LED has light distribution characteristics higher in directivity, the external radiation efficiency is greatly deteriorated, however, the external radiation efficiency of reflection-type LED does not depend upon light distribution characteristics. As described above, reflection-type LED is provided with a characteristic that light of high luminance can be radiated at a wide light distribution angle. It is considered that reflection-type LED is installed outdoors and in other place and is suitably used for a display for which high visibility is demanded and others respectively because of such a characteristic.
FIGS. 77 and 78 show a light source device 1200 using conventional type reflection-type LED. FIG. 78 is a plan viewing the light source device 1200 from the side on which light is radiated outside (from the top in FIG. 77). In the light source device 1200, after light from a light emitting element 1110 is once reflected by a reflecting mirror 1120, it is radiated outside from a radiation surface 1140. A reference number 1130 denotes an encapsulating member, 1400 and 1410 denote a lead and 1210 denotes LED.
On a display installed outdoors and in other place, when external light is taken in on the side of LED and is reflected, light (dark noise) which looks emitted from the side of LED is also observe when LED is turned off and as a result, a problem that contrast between when LED is turned on and when LED is turned off is deteriorated occurs. Then, to inhibit such dark noise and reduce the deterioration of contrast, a part except the radiation surface of LED is covered with a black or other color of member so that taking in external light on the side of LED is inhibited as much as possible. To take the light source device 1200 as an example, external light is prevented from being taken in from a place except the radiation surface 1140 by a light shielding plate 1300.
However, as shown in FIGS. 77 and 78, as the radiation surface 1140 having large area of LED 1210 is exposed to external light, the deterioration of contrast between when LED is turned on and when it is turned off due to dark noise is still left as a large problem. Such a problem occurs not only in case reflection-type LED is used but in case lens-type LED is used.
Next, a light source device 2005 using another conventional type lens-type LED is shown in FIGS. 79 and 80. FIGS. 79A and 79B show an optical path of the light source device 2005. FIG. 80 is a plan view in which the light source device 2005 is viewed from the side of external radiation of light (from the top in FIG. 79). In the light source device 2005, LED 2100 is arranged in a state that it is fitted into a through hole 2310 provided to a light shielding plate 2300. Light from a light emitting element (not shown) is radiated outside as light having a desired angle range a from the surface of the lens 2120 of an encapsulating member 2110. A reference number 2200 denotes a board on which LED 2100 is mounted.
On a display installed outdoors and in other place, when external light is taken in on the side of LED and is reflected, light (dark noise) which looks emitted from the side of LED is also observed when LED is turned off and as a result, a problem that contrast between when LED is turned on and when LED is turned off is deteriorated occurs. To inhibit such dark noise and reduce the deterioration of contrast, a part except the radiation surface of LED is covered with a black or other color of member so that taking in external light on the side of LED is inhibited as much as possible. To take the light source device 2005 as an example, external light is prevented from being taken in on the side of LED by the light shielding plate 2300.
However, the effect of external light has many problems to be improved. That is, as the surface of the lens 2120 of LED 2100 is exposed to external light, much external light is taken inside LED 2100 via the lens surface 2120. The taken external light is reflected by optics (silver plate and other on a lead frame) provided to enhance the external radiation efficiency of LED 2100 and is observed as reflected light. As a result, contrast between when LED is turned on and when LED is turned off is deteriorated.
Also, in a shop of the service industry such as a discotheque, a conventional type light emitting device is used for various projectors that emit light for gorgeously decorating the inside intentionally darkened of the shop. For one type of such a projector, there is a light pattern projector that projects a predetermined geometrical pattern on a screen and a wall.
In this type of conventional type light pattern projector, for example, a light bulb which functions as a light source is arranged in the center, a spherical light shielding curved surface is provided in a position apart from the central light source by predetermined distance R1 and a slit having a predetermined geometrical pattern is formed on the light shielding curved surface. That is, the conventional type projector is provided as a ball including a light bulb and having the radius of R1 or a semi-spherical object having a slit on the surface. Only light that passes the slit out of light emitted from the light bulb is radiated outside the projector and a light pattern corresponding to a geometrical pattern of the slit is projected on a screen which functions as a projected plane as a predetermined virtual plane installed in a position apart from the light source by predetermined distance R2 (R1<R2).
However, the conventional type light pattern projector has the following disadvantages.
Only light which is actually radiated outside and passes a slit contributes to the formation of a light pattern on a projected plane out of light emitted from a light bulb as a light source. Light which cannot pass the slit is reflected in vain inside a light shielding curved surface or absorbed, is converted to heat energy and is not effectively utilized for its proper purpose. Therefore, only a part of the quantity of light from the light source is effectively utilized and energy loss is large.
There is a limit to project the edge of a shadow by a slit. That is, when distance (R2 to R1) from the slit to a projected plane is excessively increased, compared with distance R1 from a light source to the slit, a light pattern imaged on the projected plane becomes dim. Therefore, to keep the geometrical pattern of a light pattern on the projected plane vivid to some extent, the ratio (R2/R1) of the distance R2 from the light source to the projected plane to the distance R1 from the light source to the slit is required to be kept within a predetermined range. Therefore, the fixed upper limit exists. As the distance R2 is an environmental condition of installed space itself, it is required to set the distance R1 (that is, the radius of a light pattern projector) according to the distance R2. However, in most cases, the increase of the diameter (the large-sizing) of the light pattern projector cannot be avoided.
In the conventional type light pattern projector, as a light pattern projected on a projected plane and the geometrical pattern of a slit formed on a light shielding curved surface are completely coincident, the form of a light pattern can be easily understood from the geometrical pattern of the slit before a light source is lit. When relationship between the projector and a light pattern can be extremely easily guessed as described above, an audience does not feel unexpectedness and is not interested.
Further, for an example using a conventional type light emitting device, a signal can be given. For a signal light for this type of signal, as shown in FIGS. 81 and 82A, a light bulb 3072 which is a single light source is arranged in the center of the concave surface 3071 of a reflecting mirror and a pigmented transparent filter 3073 is arranged in front of these.
As for such a signal light, a problem of pseudo-lightening is pointed out. Pseudo-lightening means a phenomenon that the light bulb looks as if it was lit by external light incident inside the signal via the pigmented transparent filter 3073 and reflected on the concave surface 3071 of the reflecting mirror though the light bulb 3072 is not lit and the phenomenon is often seen in case a signal installed with it facing west for example is exposed to the afternoon sun.
Therefore, the signal light having the light bulb 3072 as a light source is being replaced with a signal light having a lens-type light emitting diode (LED) 3075 shown in FIGS. 81 and 82B in which a light emitting element is encapsulated in a resin lens as the unit of a light source. In this signal light, plural lens-type LEDs 3075 are mounted densely in all directions on a board 3074 pigmented in black to prevent external light from being reflected. A light source in which such lens-type LEDs are densely mounted on the board is adopted not only in a signal light but in a display that displays a predetermined pattern by the emission of each LED. This LED type display has a merit that not only pseudo-lightening is solved according to it but the life is longer, compared with a display using a light bulb and the external radiation efficiency is also improved.
However, the display in which lens-type LEDs are densely mounted as described above has at least the following defects.
For the form of a lens of lens-type LED, optical design in which most of light emitted from a light emitting element can be directed in the axial direction of the lens is adopted. However, as a lens has an optical limit such as a critical angle, light to which the axial direction of the lens cannot be directed and which is not radiated outside is partially necessarily caused and all the quantity of light emitted by LED cannot be effectively utilized.
To compensate quantity emitted by individual lens-type LED, secure luminance enough for the whole display when it is turned on and secure satisfactory visibility by mounting without space, LEDs are densely mounted. However, when the mounting number of density of LEDs is enhanced, heat is confined in the display, the heat deteriorates the emission of individual LED and reduces the life of LED itself.
In a lens made of resin of lens-type LED, a small reflecting mirror (a small silver concave mirror) arranged at the back of a light emitting element is normally encapsulated together in addition to the light emitting element. Therefore, particularly in a signal light, it cannot be avoided that a part of external light incident on individual lens-type LED from the outside is reflected by the small reflecting mirror (see FIG. 82B). Therefore, when LEDs are turned off, multiple silver small spots look floating in a black board and the background color of the signal light when LEDs are turned off looks not black but grayish (this phenomenon is called dark noise). Hereby, a defect is pointed out such that the contrast of displayed color is not vivid between when LEDs are turned on and when they are turned off.
In the meantime, for a light source device, reflection-type LED where a lead on which a light emitting element is mounted is encapsulated with resin, a reflecting surface is formed on the emitting side of the light emitting element and a radiation surface is formed on the back side of the light emitting element is proposed. In this LED, a reflecting mirror is formed by depositing metal on the surface of resin formed in the shape of the reflecting surface. In LED having such structure, as substantially all the quantity of light emitted by the light emitting element can be optically controlled by the reflecting mirror, high external radiation efficiency can be realized. In case the radiation surface is formed in the shape of a convex lens, the effect of convergence can be acquired thereby.
However, it is very difficult to actually manufacture LED having such structure, it can hardly be realized or it is very troublesome and such LED is not suitable for mass production. Referring to FIGS. 83 and 84, these problems will be described below.
That is, it is very difficult to actually manufacture integrated reflection-type LED 4101 integrated in encapsulating with resin as shown in FIG. 83. The reason is that as a reflecting surface and a radiation surface are required to be respectively formed on the emitting side and on the back side of a light emitting element 4102 on the surface of encapsulating resin 4106, leads 4103a on which the light emitting element 4102 is mounted and 4103b are put between upper and lower encapsulating molds, space between the molds is filled with resin and is hardened. At this time, as a residual bubble 4107 is caused in the upper mold, a satisfactory convex form cannot be formed. As the viscosity of resin used for encapsulating LED is low even if the elimination of the residual bubble 4107 is tried by applying high pressure in filling with resin, the resin leaks from a surface joining the molds when high pressure is applied.
The LED 4111 shown in FIG. 84 according to a method of integrating after forming a convex lens 4117 separately has a problem that it takes time to align the convex lens 4117 and a light emitting part 4116 encapsulating a light emitting element 4112 with resin, it takes time to manufacture the LED and the mass production is impossible.
Further, in LED having such structure, a part of light reflected by a reflecting mirror is shielded by the light emitting element and a lead and is not radiated outside. Therefore, as the size of the light emitting element and the lead is unchanged in case LED is miniaturized, there is a problem that the ratio of shielded area to radiated area greatly increases and external radiation efficiency is greatly deteriorated. For the problem, reflection-type LED 5101 shown in FIG. 85 is proposed (in Unexamined Japanese Patent Publication No. Hei. 6-350140). This reflection-type LED 5101 is provided with a paraboloid of revolution focused on a light emitting element 5102 for the reflecting surface of a reflecting mirror 5105 except under the light emitting element 5102 and has a convex cone form 5105a only under the light emitting element 5012 so as to also radiate light radiated downward from the light emitting element 5102.
However, in the reflecting mirror 5105 having such a form, as a discontinuous sharp edge 5105b is made, the light distribution characteristics of reflected light are also discontinuous and continuous smooth radiated light cannot be acquired. There is a problem that a void is apt to be formed when such a reflecting mirror 5105 is formed with a resin mold and as the reflecting mirror has an extreme inflection point when the formation is tried by pressing a metallic plate, a non-defective product is seldom acquired and the surface roughness is also deteriorated.
In the meantime, a signal light where plural lens-type LEDs the light emitting element of each of which is encapsulated with a round-type lens are densely arranged on a board and are housed in a case is known. The signal light using LEDs for a light source has a merit that it has higher radiation efficiency, compared with that of a signal light having a light bulb generally widely used at present for a light source for emitting monochromatic light via a filter, no pseudo-lightening is caused and maintenance can be greatly reduced.
That is, in the signal light using LEDs for a light source, as LED itself emits monochromatic light, the signal light can have much higher external radiation efficiency, compared with a signal light using a light bulb that cuts most of emitted white light by a filter. In the signal light using a light bulb, when light such as the light of the afternoon sun is incident, the color of the filter is reflected, pseudo-lightening is caused, however, as no filter is required in the signal light using LED for a light source, such a problem is not caused. Further, as LED is never burnt out as a light bulb and the life is long, the frequency of maintenance can be also greatly reduced.
However, the light signal using the conventional type LED for a light source has a problem that it uses lens-type LED and the external radiation efficiency is deteriorated when the directivity of the lens-type LED is enhanced. Also, dense mounting is performed because sufficient luminous intensity and satisfactory visibility are required, however, great deal of heat is caused due to the dense mounting and LED has high temperature. It is undesirable because the output is deteriorated and the life characteristic is deteriorated that LED is turned on when it has high temperature. As optics (silver plate of a lead frame and others) for enhancing the external radiation efficiency of LED reflects external light, contrast between when LED is turned on and when it is turned off is deteriorated though no color pseudo-lightening is caused. Further, a signal light is required to save energy and has a problem that it is difficult to keep satisfactory visibility though the enhancement of the output of a light emitting element is realized in future and the number of LEDs used in a predetermined area can be reduced.
Further, a light source device in which multiple light emitting diodes (LEDs) are arranged on a board is used for illumination, a display or a signal. For LED for such a light source device, lens-type LED the diameter of which is 5 mm is widely used because sufficient light distribution characteristics are acquired. This lens-type LED is designed so that light emitted by a semiconductor light emitting element is converged by a lens and is radiated outside with directivity to some extent. Therefore, optical characteristics for approximately a multiple of the number of mounted LEDs, compared with the characteristic of single LED can be theoretically expected by arranging plural LEDs that enable external radiation on the board.
However, it is actually difficult to realize optical characteristics as in a theory. The reason is that first, there is a problem that the axial precision of individual lens-type LED is low. Particularly, in lens-type LED produced by a potting mold, the problem of the axial precision cannot be avoided. Second, when plural lens-type LEDs are mounted on a board, there is a problem that it is not necessarily easy to precisely unify the direction and the height of each LED. Particularly in the case of discrete mounting, to direct the axis of radiated light from each LED to the same direction, work for individual adjustment is often required.
Such circumstances will be concretely described below using a case that lens-type LED is applied to various light sources as an example. For example, as shown in FIG. 86, a light source device using conventional type lens-type LED is formed by inserting a lead 6074 of the lens-type LED 6073 into a hole 6072 formed beforehand through a single mounting board 6071 and soldering each, lead 6074 with the board 6071.
In such a light source, the enhancement of the mounting number of density per unit area is demanded to secure sufficient luminance and some hundred LEDs 6073 may be mounted on one mounting board 6071 in the case of a light source device for a signal light. In a light source device used in photography by a CCD camera for example, the mounting number of density of LEDs 6073 per unit area is further enhanced, compared with the light source device for a signal light. In this light source device, each LED 6073 is mounted on the mounting board 6071 in a state that looks as if the respective were in contact.
The lens-type LED 6073 shown in FIG. 86 is generally manufactured using a potting mold. Potting means a method of mounting a semiconductor light emitting element 6075 at the end as shown in FIG. 87, arranging a pair of leads 6074 conducted via the semiconductor light emitting element 6075 and bonding wire 6076 in a resin forming case (a pot) 6077 and manufacturing LED encapsulating the semiconductor light emitting element 6075 inside a lens 6078 shown in FIG. 86 and made of transparent resin by pouring liquid resin into the resin forming case for thermosetting. The outline of the potting molding is disclosed in Japanese published unexamined patent application No. Hei 7-183440 for example. In lens-type LED 6073 manufactured using the potting mold, a pair of leads 6074 is extended in parallel with the axial direction of the lens 6078 from the lens 6078 made of resin.
For the conventional type LED light source, the following defects are pointed out. First, in discrete mounting, in case the mounting number of density is extremely high as in the light source device used in photography by a CCD camera, automatic dense mounting using an automechanism (or a robot) is difficult. Therefore, extremely dense discrete mounting may be required to depend upon manual labor. Manual work generally takes much time for mounting work. It is difficult to unify the height and the mounting angle of lens-type LED mounted on a board and the height and the mounting angle of LED are apt to be uneven. Therefore, the aggregate of LEDs may be unable to fully emit (because the light distribution characteristics become unstable). There is a problem that it takes further much time to adjust the light distribution characteristics.
As also pointed out in Unexamined Japanese Patent Publication No. Hei. 7-183440, generally in potting molding, the leads 6074 (and its frame) are apt to tilt for the pot 6077 when resin is cast and in completed individual. LED 6073, dislocation is apt to be caused between the central axis of the lens 6078 and the optical axis of light radiated from the light emitting element 6075. That is, it is difficult to enhance the axial precision of the lens-type LED 6073 itself which is an attachment.
As described above, it need scarcely be said that it takes much manual labor when lens-type LEDs 6073 are discretely mounted on the board 6071, after mounting, work for individual adjustment such as the mounting angle of individual LED 6073 is manually finely controlled is also essential to unify the radiation direction of light from each LED 6073 and the low productivity comes into a question.
For a method of manufacturing LED, securing the high positional precision of a lens for a light emitting element, the application of a transfer mold is heretofore proposed. In transfer molding, liquid resin is poured into a cavity of the molds in a state that a lead frame is fixed between a pair of molds when a light emitting element is encapsulated with resin so as to form a lens.
However, for LED manufacturing according to transfer molding, to acquire sufficient light distribution effect, a lens is also required to be formed so that it has the diameter of 5 mm or more. LED manufactured according to transfer molding requires more quantity of encapsulating resin, compared with LED 6073 manufactured according to the potting molding and provided with the lens 6078 of approximately the same size. Therefore, in mounting LED, encapsulating resin is greatly thermally deformed by heat history in thermosetting processing using cream solder for fixing the leads of LED on a board and a problem such as the disconnection of bonding wire may occur.